Re: obtaining row locking information

Tatsuo, have you developed a new version of this for 8.2?

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Tatsuo Ishii wrote:
> > Tatsuo Ishii <t-ishii@sra.co.jp> writes:
> > > To accomplish this I need to add following function into
> > > storage/ipc/procarray.c. This is similar to BackendPidGetProc() except
> > > that it accepts xid as an argument. Any objection?
> > 
> > >     if (xid == 0)                /* never match dummy PGPROCs */
> > >         return NULL;
> > 
> > I think this test should be against InvalidTransactionId, not "0", and
> > the comment is wrong (you are suppressing matches against idle PGPROCs).
> > 
> > Also note the comment at the top of the function: once you release
> > ProcArrayLock you have no guarantee that the result means anything at
> > all; and unlike ProcSendSignal, you have no reason to think that the
> > target backend can't quit before you get another cycle.  It might be
> > better to return the pid directly rather than assuming it'll still be
> > meaningful to indirect through a returned pointer.
> 
> Agreed.
> 
> > Also, what are you going to do about prepared transactions?  They can
> > hold locks but they don't have PIDs.  On the whole, I'm not sure this
> > is a good idea at all, because of that.
> 
> For prepared transactions, just showing "0" pids are enough, I
> think. Assuming that in practice most transactions are not prepared
> ones, I think the function is not perfect, but is usefull enough for
> most DBAs.
> --
> Tatsuo Ishii
> 

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